Download Lecture 11 Mating systems 4 slides per page

Assignment 4
Assignment 4: Constructing an Ethogram and Hypotheses about
Animal Behavior
1. The goal of this assignment is to have you apply your knowledge
of behavioral ecology to behaviors that you personally observe.
a. First, you will quantify behavioral observations using an
ethogram. You will use your ethogram to construct a “behavior
budget” that describes how often the animal performs each
behavior.
b. Second, you will generate a hypothesis about your behavioral
observations and propose a way to experimentally test
your hypothesis.
Assignment 4
Example Ethogram from MacNulty 2007
Assignment 4
Assignment 4: Constructing an Ethogram and Hypotheses about
Animal Behavior
5. Develop a hypothesis or set of hypotheses about one or more of the
behaviors that you observed. The hypothesis should deal with a
reason why the animal that you observed exhibited the behavior or
behavioral budget that you documented. You should have both a null
and alternative hypothesis.
6. Develop a hypothetical experiment or set of experiments that could be
used to test your hypothesis. A good source of inspiration of possible
experiments are the studies discussed in class. Note that your
experiments should be feasible for one person to do with a budget of
up to $10,000 (the budget of many graduate student projects) in the
time frame of one year. Proposing to do a breeding experiment with
elephant seals is not feasible because they are not easily manipulated.
Love Darts in Snails and Slugs
1. During copulation, partners place large spermatophores in the
spermatophore-receiving (SRO) organ of their partner.
2. The spermatophore is then digested in the SRO. Only ~0.1% of
the spermatozoa escapes to where fertilization occurs.
3. Individuals shoot each other with love darts. The love dart is
laced with hormones and increases the number of escaping
spermatozoa from the SRO
4. By darting its partner, a snail can increase its chances of
paternity.
5. The Japanese Euhadra subnimbosa uses its darts to stab
its partner >3000 times during 22 min of ‘foreplay’ before
copulation.
Diversity in Love Darts
Lesson: Sexual conflict can lead to diversification.
Love Darts in Snails and Slugs
1. Darts have evolved multiple times, and have been lost multiple
times.
2. Darting species may be locked in sexually antagonistic selection
which leads to an arms race of defense/offense.
a. SRO complexity correlates positively with dart shape (e.g. the
presence of flanges).
Hermaphroditic flatworm, Pseudobiceros bedfordi.
Have two penises, which they fence with. Each tries to smear the other
with sperm, but tries to avoid getting smeared.
Hermaphroditic flatworm, Pseudobiceros bedfordi.
St = areas with sperm
Hermaphroditic flatworm, Pseudobiceros bedfordi.
H = holes caused by sperm, Sc = Scars
Hermaphroditic flatworm, Pseudobiceros bedfordi.
* = Large hole where large amount of sperm hit
Body then tore in two!
Lessons
1. Sexual conflict can be costly. Can impose a large selective
force. Can lead to partner manipulation.
2. Even hermaphrodites have different interests when mating.
Each is trying to maximize its individual fitness.
3. Sexual antagonism can select for diversity in weapons and
mating behaviors.
Mediating the Conflict
1. Many hermaphrodites inseminate reciprocally. This “sperm
trading” ensures reciprocity during mating.
2. Test: Create cheaters by vasectomizing one partner of
hermaphroditic sea slugs (Study by Anthes, 2005)
3. Result: Partners of the cheaters were
less likely to trade intromissions/inseminations,
and were more likely to terminate a mating
encounter.
Further Reading on Wacky Mating Systems:
Dr. Tatiana’s Sex Advice to all Creation
Lecture Outline: Mating Systems
Diversity among species
Basic Categories of Mating Systems and How they are determined
by ecology.
Diversity within species
Alternative mating strategies and their evolution.
Reminder: Assignment 2 is due on Wednesday
Basic Categories of Mating Systems
1. Monogamy: A male and female form a pair bond (short or long
term). Often both parents care for eggs/young.
2. Polygyny: A male mates with several females. Females mate
with just one male. Usually female provides parental care.
3. Polyandry: A female mates with several males. Often the male
provides parental care.
4. Promiscuity: Both males and females mate several times with
different individuals. Either sex may care for the young.
5. Polygamy: a general term for when an individual of either sex
has more than one mate.
Ecological Theory of Mating System Evolution
Emlen and Oring, 1977
1. Mating systems depend on the ability of a portion of the
population to control the access of others to potential mates.
2. Multiple mates must be energetically defendable by individuals
a. Even distribution of mates = little polygamy potential.
b. Patchy distribution = high polygamy potential.
Ecological Theory of Mating System Evolution
Emlen and Oring, 1977
3. Benefits of defense must outweigh the costs.
a. Energy spent defending or seeking mates comes at the cost
of parental care.
4. Environmental factors determine the costs and benefits. For
instance, how females are spaced.
5. Ecology constrains the degree to which sexual selection can
operate.
Monogamy
1. Sexual selection theory suggests that a male’s reproductive
success is usually related to the number of females he
inseminates.
2. Why monogamy?
Hypotheses for Monogamy
1. Mate guarding hypothesis: Monogamy may be adaptive if a
female left by the male would probably acquire another mate
who would fertilize her eggs.
2. Mate guarding likely to occur if females are receptive after
mating, widely scattered, and difficult to locate.
3. Example: Clown shrimp, females are widely dispersed, males
spend weeks with a female.
Hypotheses for Monogamy
1. Mate assistance hypothesis: Males stay with a single female to
help rear their mutual offspring.
2. The additional offspring that survive due to paternal care may
more than compensate the male for the chance to reproduce
with other females.
3. Example: Seahorse Hippocampus whitei, pairs ignore any
others of the opposite sex. The male’s pouch can only hold 1
clutch of eggs, so as long as his pouch is full he is maximizing
his reproduction.
4. Example: Monogamous California mice, males help
rear offspring. ~2 offspring born. With male: 1.5 on
average survive. Without male: .6 on average
survive.
Hypotheses for Monogamy
1. Female enforced monogamy: Females attempt to block their
partners’ polygynous moves in order to monopolize their parental
assistance.
2. Example: Razorbills (a seabird), females attack their partner if
they show interest in a neighbor.
Monogamy
2. Example: Burying beetles. Male and female bury a mouse to
feed offspring. Once buried, the male may release a
pheromone to attract other females. His mate pushes him from
his perch, reducing his ability to signal. (from Eggert and
Skaluk, 1995).
Social vs Genetic Monogamy
1. About 90% of all birds are socially monogamous: form long-term
partnerships during a breeding system.
a. Male birds (unlike many mammals) can increase fitness
substantially by helping with eggs/nestlings. Mate
assistance hypothesis.
2. In some birds social monogamy = genetic monogamy. Ex.
Common loons and Florida scrub jays.
3. Many socially monogamous birds have extra pair copulations
(EPCs). Not genetically monogamous.
4. EPCs benefit males by allowing him to sire offspring. Tradeoff is
while he is gone, he gives up mate guarding.
Females and EPCs
1. What do females gain from EPCs?
2. Good genes hypothesis: Gain good genes for offspring.
a. Female tits seek EPCs if mated to an unattractive partner (ie
the partner gets few EPCs).
3. Fertility insurance hypothesis: EPCs reduce risk of having
infertile parter. Test = look at fertilization success.
a. Gunnison’s praire dogs: Polyandrous females: pregnant
100% of time, monogamous females: pregnant 92% of the
time.
3. More resources hypothesis: Mating with multiple males allows
access to more resources.
a. Dunnocks: Females seek out a subordinate mate. Will
copulate 100s of times for a clutch of eggs. Both males help
rear the offspring.
Polyandry
1. Galapagos hawks: As many as 8 males may pair with a female,
helping her rear a single offspring per breeding episode.
a. Suitable breeding territories are scarce, males may
cooperate to keep other males out, all males have an equal
chance of fertilization.
Polyandry
1. Spotted sandpipers
a. Females fight other females for territories.
b. A territory may attract more than one male who incubate a
single female’s clutches.
c. This “sex role reversal” could be due to female only being
able to lay 4 eggs at a time. If resources are abundant, they
need another mate to take care of another clutch.
d. Food is often abundant.
Female Defense Polygyny
1. Female defense polygyny: Females occur in defensible clusters,
males compete for control of the clusters.
2. Examples:
a. Male Greater Spear-Nosed Bats defend roosting females.
Successful defenders may sire up to 50 offspring.
Female Defense Polygyny
b. A marine amphipod: Forms a house out of shells and
pebbles. Males capture females and glue their houses to
his!
Resource Defense Polygyny
1. Resource defense polygyny:
a. Females do not live together permanently.
b. Male may become polygynous if he controls a rich patch of
resources that the female’s visit
2. Examples:
a. Male black-winged damselflies defend floating vegetation.
Females mate with the male and lay eggs on the vegetation.
Resource Defense Polygyny
Example 2
a. African cichlid fish, Lamprologus callipterus. Need safe
location for eggs.
b. Female lays eggs in an empty snail shell, and guards them.
c. Males collect shells, sometimes stealing them from rival
males. Observed to collect up to 86 shells. Up to 14 females
nesting on one male’s territory
Testing Resource Defense Polygyny
1. Predicts that female distribution is controlled by key resources
2. Test = Manipulate the resources, see if females alter their
locations.
3. Example: Dunnocks (a songbird), Davies and Lundberg
a. Normally females search for food widely. This means that
female go on multiple males territories. They are
polyandrous.
b. Experiment: Supplemented some home ranges with food.
Testing Resource Defense Polygyny
Result: With supplemented food, females decreased their range
size. This decreased the number of mates that they had. Males
were able to monopolize females.
Scramble Competition Polygyny
1. Scramble competition polygyny: Females are widely dispersed,
which reduces the benefits of territorial behavior. Males try to
outrace rivals to receptive females.
2. Examples:
a. Male thirteen-lined squirrels search widely for females that
are receptive for 4-5 hours during the breeding season.
Males bias their searching at places where a female was
about to go into estrous.
Scramble Competition Polygyny
Example 2: Explosive breeding assemblages
a. Horseshoe crabs: Females lay eggs during just a few nights.
Males scramble to get a mate.
b. Wood frogs: Females lay eggs in just one or a few nights.
The high density of females and rival males does not make
territoriality feasible.
Lek Polygyny
1. Lek Polygyny: Sometimes males advertise to females with
elaborate visual, acoustic, or olfactory displays. Males do not
hunt for mates. Females watch males display at territories that
do not contain food, nesting sites, or anything useful.
2. Sometimes males aggregate into groups and each male defends
a small territory that contains no resources at all-sometimes just
a bare patch of ground.
a. When territories are clumped in a display area = a lek.
2. Male mating success is highly skewed on lecks
a. Manakins: males jump between perches, snapping. feathers.
At a lek of 10, there were 438 copulations. One male = 75%,
second male = 13%, six others = 10%.
Leks
Mating success if usually strongly skewed on leks with the majority of matings
going to a small proportion of males.
36
Leks
1. Leks have been reported in only 7 species of mammals and 35
species of birds
2. Thought to occur when males are unable to defend
economically either the females themselves or the resources they
require
a. In both antelope and grouse, the lekking species are those
with the largest female home ranges
b. In Uganda kob, topi and fallow deer, males lek at high
population densities but defend territories or harems at low
densities
Why Lek?
1. Why do males all congregate to display? Lots of competition.
2. Hotspot hypothesis: females tend to travel along certain routes
and males congregate where routes intersect.
3. Hotshot hypothesis: subordinate males cluster around highly
attractive males hoping to interact with females attracted to the
hotshots.
4. Test: Remove males that were successful in attracting females.
a. Hotspot prediction = other males will move into best site.
b. Hotshot prediction = subordinates will leave site.
5. Example: Great snipe. Removal of dominant male caused
subordinates to leave. Removal of a subordinate resulted in
another subordinate coming in.
Why Lek?
6. Female preference hypothesis: females prefer groups of large
males where they can more quickly compare the quality of
males.
7. Test: Look at whether reproductive success varies with number
of males at lek.
8. Example: Ruffs (a sandpiper). More males attract more females
up to a point. After 6 or more males, the dominant’s
reproductive success goes down.
Why Lek?
9. Reducing male predation hypothesis: As lek size increases likelihood of any
one male being predated decreases (dilution effect)
a. Tungara frogs are safer from bat predation when calling in large choruses
(panel a).
10. Increased female attraction hypothesis: By displaying together males provide
greater attraction for females and draw them in from a greater distance
a. Tungara frog payoffs per individual male increased with lek size (panel b).
11. These hypotheses are not exclusive and many be important depending on
species and spatial scale.
Alternative Mating Systems
1. Monopolization of females by males, leaves many males without
a mate.
2. This can favor the evolution of sneaking strategies. Often get
“female mimics.”
3. Traits favored for sneaking may differ from those of territorial
males. Often different morphs become markedly distinct.
4. Selection is often frequency dependent selection. The rare
types have a fitness advantage. This leads to the stable
maintenance of multiple morphs.
a. Prediction: over time the fitnesses of the strategies should be
about equal.
5. Can be polymorphic, polyphenic, or plastically determined.
Polymorphic side-blotched lizard strategies
Orange Morph: Territory Usurper
Large size
Large territories
Tradeoff: Low survival to next year
Yellow Morph: Sneaker
Mimics females
Not territorial
Blue Morph: Mate Guarder
Small territories
Sinervo & Lively 1996, Zamudio & Sinervo 2000, Sinervo et al 2000, Sinervo & Svensson 2002,
Sinervo & Clobert, 2003, Sinervo et. al. 2006
Selection on males is frequency dependent:
rock-paper-scissors
Alternative Mating Strategies
Marine Isopod Morphs
Shuster and Wade
1. Male types are a polymorphism.
a. Alpha males: Have pincers and defend sponges.
b. Beta males: Female mimics
c. Gamma males: Invest in sperm, dive into matings.
2. Mating success approximately equal: Alpha = 1.51 mates, Beta
= 1.35 mates, gamma = 1.37 mates.
Dung Beetle Mating Strategies
Emlen & Nijhout
1. Male types are a polyphenism. Morphology (horns/no horns) is
plastically determined by the amount of dung the larva was
raised on.
2. Mating behavior is variable: defend or sneak.
3. Developmental tradeoff: Big horns can mean small eyes!
Plastic Natterjack Toad Mating Strategies
1. Male types are plastic. Males make the “best of a bad job” =
makes best of poor circumstances by adopting alternative
strategy.
2. Large males call loudly and attract the most females. 60% were
callers, but got 80% of matings.
3. Small males are “satellites” and attempt to intercept females.
Will switch behaviors when they get bigger. Also, if remove the
large males, then they will call.